With respect to the associated technical field, in addition to German Patent Documents DE 101 13 000 A1 (U.S. Pat. No. 6,918,365) and DE 199 13 795 C1 as well as German Patent Application 2004 048 526, which is no prior publication, reference is made particularly to German Patent Document DE 100 54 007 A1 (U.S. Pat. No. 6,588,211).
Particularly for the use in motor vehicles, it could be an interesting concept for the future to combine an internal-combustion engine operating as a vehicle drive assembly and a fuel cell generating electric energy either only in the form of an APU (=auxiliary power unit) or even for an electromotive drive, which would then be designed as a so-called hybrid drive. Various suggestions already exist as to how the fuel cell and the internal-combustion engine can be thermally coupled with one another in such a manner that the waste heat of one of these two units can be utilized by the other unit.
German Patent Document DE 101 13 000 A1 suggests a thermal coupling between the housing of the internal-combustion engine, that is, the so-called engine block, and the fuel cell in order to utilize the waste heat and in the process particularly the residual heat of the fuel cell during a vehicle stoppage for the temperature equalization of the internal-combustion engine. According to German Patent Document DE 199 13 795 C1, the fuel cell and internal-combustion engine units have a number of components in common, such as the radiator, the exhaust gas system and the air filters. In this case, the fuel cell system can be heated by the exhaust gases of the internal-combustion engine, specifically by means of one or more suitable heat exchanger(s) through which air or fuel for the fuel cell is carried. According to German Patent Document 100 54 007 A1, energy flows and/or substance flows of a driving internal-combustion engine of a motor vehicle are coupled with those of the fuel cell system.
Hereby, it is to be demonstrated how such a basically known thermal coupling between a fuel cell and an internal-combustion engine can be still further increased and can therefore be improved, which is one object of the present invention.
This object is achieved for a system consisting of a fuel cell and of an internal-combustion engine in an arrangement where the exhaust gas of the internal-combustion engine flows around the fuel cell. Advantageous embodiments and further developments are described herein.
A heat-transferring connection between the exhaust gas flow of an internal-combustion engine and a fuel cell, or the air flow or fuel flow supplied to the latter is basically known. However, in the present invention a direct heat transfer is provided between the exhaust gas of the internal-combustion engine and the fuel cell, specifically in that the exhaust gas of the internal-combustion engine flows around the fuel cell or a corresponding housing of the latter, in which housing, among other things, the gas flows reacting with one another by way of the electrodes of the fuel cell are guided by way of these electrodes. For a fast heating of the fuel cell, for example, a solid oxide fuel cell (SOFC), whose operating temperature, as known, is in the order of from 600° C. to 800° C., the relatively hot exhaust gas flow of the internal-combustion engine is extremely helpful, if the operation of the latter is started before or simultaneously with that of the fuel cell. Naturally, the fuel cell can also be appropriately equalized in its temperature for its entire operating duration as a result of the exhaust gas flow of the internal-combustion engine.
The heat transfer between the internal-combustion engine exhaust gas and the fuel cell in this quasi direct manner takes place much more rapidly and efficiently than indirect methods using heat exchangers, although the last-mentioned heat-transferring connection by way of heat exchangers (specifically by way of a fluid flow fed to the fuel cell) may be provided in an additional and supporting fashion. Thus, in addition to the direct heat transfer between the exhaust gas of the internal-combustion engine and the fuel cell first suggested here, a heat-transferring connection may be provided by way of a heat exchanger (or the like), such that exhaust gases of the internal-combustion engine are in a heat-transferring connection with the air flow or fuel flow fed to the fuel cell. The same applies to the exhaust gases of the fuel cell; that is, the heat contained in the latter can also be partially returned to the fuel cell by way of a heat exchange with another fluid flow.
Advantageously, the basic suggestion of the present invention, specifically the suggestion of at least essentially letting the exhaust gas of the internal-combustion engine flow around the fuel cell or its housing, leads to a reduced insulation requirement at the fuel cell or at its periphery (housing, supply lines, etc.), since, on the one hand, the loss of heat of the fuel cell is reduced because of the slight temperature difference between the fuel cell and the exhaust gas flow surrounding the latter and, on the other hand, an exhaust gas system carrying the exhaust gas flow of the internal-combustion engine in the case of the (preferred) use in a motor vehicle normally is already sufficiently insulated toward the latter. Thus, advantageously, virtually no additional insulation measures for the protection of the vehicle or its components will be required in view of the temperatures of the fuel cell system.
For implementing the suggestion of letting the exhaust gas flow of an internal-combustion engine flow at least essentially around a fuel cell, the fuel cell or its housing may be at least essentially integrated in the exhaust gas system carrying the exhaust gases of the internal-combustion engine; that is, it may, for example, be arranged inside a correspondingly designed pipe having a correspondingly enlarged cross-section, or in a wall section of a hollow body operating as an exhaust-gas-carrying pipe. At least for those embodiments of the invention in which the fuel cell or its housing is arranged upstream of an exhaust gas treatment system or an exhaust gas purification system in the exhaust gas system of the internal-combustion engine, the fuel cell or its waste heat can be utilized for bringing this exhaust gas treatment system, which may, for example, by a 3-way catalyst or a particle filter or a DeNOx catalyst, faster to its operating temperature, or for burning this exhaust gas treatment system (particularly in the form of a particle filter or a DeNOx catalyst) free. This is particularly so when the exhaust gas of the fuel cell had previously been afterburnt or further heated in a so-called afterburner. (The latter is basically known to a person skilled in the art). A corresponding operating method is therefore characterized in that, preferably after a further treatment in an afterburner, the exhaust gas of the fuel cell is fed in a targeted manner to an exhaust gas purification system for its regenerating, which exhaust gas purification system, as a matter of priority, is assigned to the internal-combustion engine.
In addition to flowing around the fuel cell, the exhaust gas flow of the internal-combustion engine can also at least essentially flow around an afterburner for the exhaust gas of the fuel cell and/or around a reformer for processing its fuel, or these above-mentioned units may correspondingly at least essentially be arranged inside the exhaust gas system of the internal-combustion engine. As a result, also these elements can be heated or insulated in a simple manner, or it becomes easily possible to connect the fuel cell with these elements, or their waste heat can easily and efficiently be utilized for the internal-combustion engine or its exhaust gas purification system. This is so at least if the fuel cell or the fuel cell and a reformer is/are arranged upstream of an exhaust gas purification system for the internal-combustion engine exhaust gases at least essentially inside a pipe or the like carrying them. Advantageously, the exhaust gases of the fuel cell can thereby be treated in the exhaust gas purification system, so that an independent afterburner is no longer required for this purpose. As an alternative, the fuel cell or the fuel cell and/or an afterburner and/or a reformer (for processing the fuel) may be arranged downstream of an exhaust gas purification system for the internal-combustion engine exhaust gases at least essentially inside a pipe carrying the latter.
According to an advantageous further development, at least a portion of the exhaust gas flow of the fuel cell can be fed to the internal-combustion engine for the combustion or can generally be fed to an exhaust gas recirculation device of the internal-combustion engine. In this manner, unburnt residual fuel, which could be contained in the fuel cell exhaust gas, can be meaningfully utilized, specifically burnt in the internal-combustion engine while releasing mechanical energy. Additionally, the exhaust gas emissions of the internal-combustion engine may be simultaneously reduced. Furthermore, the temperature level of the internal combustion engine or of the exhaust gas recirculation device can thereby be kept within a desired range. However, at least a portion of the exhaust gas of the internal-combustion engine can also be supplied directly to the reformer or to a reformer for the processing of fuel for the fuel cell, in this case, the constituents of this exhaust gas can be utilized in the reformer.
Incidentally, the thermal energy of the exhaust gas of the fuel cell and/or of the internal-combustion engine may not only—as indicated above—be used in a heat exchanger for heating the fresh-air flow supplied to the fuel cell but—also in a suitable heat exchanger—for preheating fuel, particularly in the event that fuel intended for the internal-combustion engine is fed to a reformer for the processing of fuel for the fuel cell, in which case, this fuel is pre-evaporated upstream of the reformer in a heat exchanger.